Electron gun for electron irradiation equipment

ABSTRACT

An electron gun for use in electron irradiation equipment. The gun comprises a cartridge including a Wehnelt electrode and a filament with two plug electrodes mounted on an insulating plate. The filament is mounted between the Wehnelt electrode and a conductive plate by two fasteners and can be adjustably aligned with respect to the Wehnelt electrode by moving the electrode with respect to the filament before the mounting is made fast. The electrical potential supply terminal has two jacks which receive the plug electrodes thereby mechanically and electrically coupling the cartridge to the potential supply and the Wehnelt electrode receives its potential through a resilient contact on the potential supply terminal.

United States Patent Shirai et al.

ELECTRON GUN FOR ELECTRON IRRADIATION EQUIPMENT Inventors: Shogo Shirai,Yokohama; Haruo Uchida, Tokyo, both of Japan Assignee: Kabushiki KaishaAkashi Seisakusho, Tokyo, Japan Filed: May 17, 1973 Appl. No.: 361,180

Foreign Application Priority Data May 22, 1972 Japan 47-50587 US. Cl313/237, 313/49, 313/82 R,

, 313/821 1111.01. H01j 1/00 Field of Search 313/49, 236, 237, 82, 82.1

6/1965 Sciaky 2/l968 Douglass ..3l3/fl9X 6/1971 Hogg 313/237 8/1971 Neis313 237 Primary ExaminerArchie R. Borchelt Assistant Examiner-SaxfieldChatmon, Jr. Attorney, Agent, or Firm-Robert E. Burns; Emmanuel J.Lobato; Bruce L. Adams [5 7 ABSTRACT An electron gun for use in electronirradiation equipment. The gun comprises a cartridge including a Wehneltelectrode and a filament with two plug electrodes mounted on aninsulating plate. The filament is mounted between the Wehnelt electrodeand a conductive plate by two fasteners and can be adjustably alignedwith respect to the Wehnelt electrode by moving the electrode withrespect to the filament before the mounting is made fast. .Theelectrical potential supply terminal has two jacks which receive theplug electrodes thereby mechanically and electrically coupling thecartridge to the potential supply and the Wehnelt electrode receives itspotential through a resilient contact on the potential supply terminal.

Patented Dec. 24, 1974 3,857,055

FIG. E

PRIOR ART FIG 2 ELECTRON GUN FOR ELECTRON, IRRADIATION EQUIPMENTBACKGROUND OF THE INVENTION used for electron irradiation equipment, arelarge in 7 size as a result of their complex structure and thus havehigh manufacturing costs.

The conventional electron guns comprise an electrode assembly and afilament which are mounted separately and thus necessitate alignment ofthe filament and the electrode each time the electron gun is assembled.

The alignment of the filamant and the electrode in the prior artelectron guns is not reliable when the filament becomes heated, sincethe alignment is sensitive to the thermal expansion of the various partsof the electron gun.

The conventional electron guns also have the disadvantage that theconnections between the power supply and the various electrodes iscomplicated and the voltage applied to the electrode assembly isgenerally through the various parts of the mounting structure.

SUMMARY OF THE INVENTION The main object of the present invention is tosolve the aforementioned problems of the conventional electron guns byproviding an electron gun*for use in electron irradiation equipmentwhich has a simple construction and is small in size. 7

It is another object of the present'invention to provide and electrongun which permits easy and positive alignment of the filament tip withrespect to the main electrode.

A further object of the present invention is to provide an electron guncomprising a cartridge comprising a filament having two plug electrodesand a main electrode, where the cartridge is both mechanically andelectrically detachably coupled to the supply terminal for supplyingelectric potential to the cartridge.

These and other objects of the invention are carried out by the electrongun comprising a cartridge comprising a filament having two plugelectrodes, a main electrode and means connecting the filament to themain electrode and for aligning the filament with the main electrode.The electron gun also comprises supply terminal means for supplyingelectric potential to the main electrode and to the two plug electrodesand includes jack means for detachably coupling the two, plug electrodesboth mechanically and electrically to the supply terminal means andmeans separate from the jack means for detachably electrically couplingthe main electrodes to the supply terminal means.

The-cartridge includes an insulating plate member that has the twoelectrodes'mounted thereon and projecting therefrom on one side thereof.At least one fastener is received through an aperture in the insulatingplate member with a clearance thereabout to permit adjustable movementof the main electrode with respect to the insulating plate memberthereby providing for the adjustable positioning of the main electrodewith respect to-the filament. The supply terminal means has jack meansthat receive the two plug electrodes therein for mechanically couplingthe cartridge to the supply terminal means. This means for electricallycoupling the main electrode comprises a resilient contact electricallycontacting the main electrode when the cartridge is mechanically coupledto the supply termainal means and means biasing the electrical contactoutwardly of the supply terminal means.

l-Iaving in mind the above and other objects that will be obvious froman understanding of the disclosure, the present invention comprises acombination and arrangement of parts illustrated in the presentlypreferred embodiments of the invention which are hereinafter set forthin sufficient detail to enable those persons skilled in the art toclearly understand the function, operation, construction and advantagesof it when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view ofa'conventional electron gun for use in electron irradiation equipment. I

FIG. 2 is a sectional view of an electron gun for use in electronirradiation equipment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows anexample of aconventional electron gun for use in electron irradiation equipment inwhich a pair of electrodes 2, are attached to a filament 1 by spotwelding. The electrodes 2, are fixed to an insulating plate 3 andconnected to a pair of of terminals 6 on an insulating block 5 by anintermediate conductor member 4.

The middle portion of a metal cylinder 7 holds insulating block 5, in anadjustable position which may be varied by use of an adjusting screw 5a.The lower portion of cylinder 7 has a Wehnelt electrode 8 screwmountedthereon. The electrode 8 has a small hole through which electron beamspass. The upper portion of the cylinder '7 has a flange 7a on which afastening ring 9 is rotatably fitted for connecting the assembly to theremaining structure.

A metal fittingl2 is fluidtightly fixed through a seal 11 to a flange10a formed at the lower end of an electron gun insulator l0. The'upperend portion of ring 9 has an internal thread which engages an externalthread of a portion of the lower end of metal fitting 12, so thatturning the ring 9 fastens the upper flange 7a of said cylinder 7 to thelower end of the metal fitting 12.

When so fastened, an elastic metal tongue 6a, which is attached to theupper portion of each terminal 6, is pressed against terminal 14 whichis fitted through an insulating material 13 in such a manner as to sealthe central opening in the metal fitting 12. The terminal 14 isconnected to a power source (not shown).

The metal fitting 12 is connected to a voltage supply (not shown) bywire 15 for applying the voltage to the Wehnelt electrode 8. The voltageis applied to the Wehnelt electrode 8 through said metal cylinder 7.

One disadvantage of the electron gun, as described above, is that theinsulating block 5 is adjusted by the adjusting screw 50 prior to use ofthe electron gun, and the tip of the filament I is thereby aligned tothe small hole 8a in the Wehnelt electrode 8. In spite of thepreliminary adjustment, when the filament 1 becomes heated afterenergization, the metal cylinder 7 undergoes thermal expansion therebyvarying the alignment between the filament tip and the hole 8a.

In addition since the electron gun has a complicated structure and iscostly, when the filament 1 has'been consumed, a block comprising thefilament 1, electrodes 2 and insulating plate 3 must be replaced byremoving the Wehnelt electrode 8. This necessitates another alignment ofthe tip of the filament 1 and the small hole 8a in the Wehnelt electrodefor each replacement.

A further disadvantage of the conventional electron gun, as describedwith reference to FIG. 1, is that voltage from the power source isapplied to the Wehnelt electrode 8 through the electric wire 15, metalfitting 12, ring 9 and the metal cylinder 7. This contributes tocomplexity of construction of the electron gun.

An embodiment of the electron gun according to the invention will now bedescribed by reference to FIG. 2. FIG. 2 is a sectional view of theelectron gun, in which both ends of a V-shaped filament 21 are-fixed byspot welding to the lower ends of a pair of plug or bar electrodes 22which pass through and are sealed in by glass to an insulating plate 23composed of steatite or other similar material. Insulating plate 23 maybe made of mica, and the electrodes 22 may be fastened thereto by nuts.The insulating plate 23 correspondes to insulating plate 3 of the priorart electron gun described before.

A Wehnelt electrode 24 has a small hole 24a at the center thereofto'pass electron beams through and has a portion or flange surface ofthe insulating plate 23 or the filament side thereof. The insulatingplate 23is held between the Wehnelt electrode 24 'and a conductive metaldoubling plate 25fastened together by a clamping bolt 26. The clampingbolt26 screws into a tapped hole 25a in the doubling plate 25 through ahole in the flange of the Wehnelt electrode 24 and a clearance hole 23ain the insulating plate 23. By fastening the clamping bolt 26, theWehnelt electrode 24 can be fixed in'close contact with the insulatingplate 23.

When fastening the clamping bolt 26, the position of the Wehneltelectrode 24 with-respect to the'insulating plate 23 can be adjusted byutilizing the clearance hole 23a in the insulating plate 23. By thismeans, alignment of the tip 210 of the filament 21 and the small hole 24in the Wehnelt electrode can be effected.

Each filament electrode 22 passes through the insulating plate 23, andthrough a hole 25b without coming in contact with the doubling plate 25,and forms a projected end 22a on the side of the insulating plate 23oppositethe filament 21. The'projected ends are detachably coupled asplugs in jack 28 fixed to an electron gun insulator 27. Thus whenelectrodes 22a are received in jack 28, the filament is bothelectrically and mechanically coupled thereto.

A Wehnelt terminal 29 has a specified voltage applied thereto and isfixed to the electron gun insulator 27. Terminal 29 has a spring contact30 attached to the lower end thereof which resiliently presses againstthe metal doubling plate 25. This meansthat the specified voltage isapplied from the Wehnelt terminal 29 to the Wehnelt electrode 24 throughsaid spring contact 30, metal doubling plate 25 and clamping bolt 26.

During operation of the electron gun in electron irradiation equipmentsuch as scanning type electron microscopes, the inside of the electrongun insulator 27 tion in size of the Wehnelt electrode and alsomaintains is kept at atmospheric pressure and the filament 21 is in avacuum.

For example, in a small scanning type electronic microscope 3 volts ofvoltage is applied and 2 amperes of current flows between the electrodes22 connected to the filament 21. Under this condition, thermoelectronsproduced at the filament 21 are controlled by the Wehnelt electrode 24with a potential difference of, for example, of some 500 volts lowerthan the filament potential. The electrons are accelerated and inducedthrough the small hole- 24a .toward an anode (not shown) which hasapotential difference of, for example, some 10 kilovolts higher than thefilament potential.

During maintenance of the electron gun, in which there is an inspectionor adjustment made, the filament 21 is put at atmospheric pressure, andthe projected ends 220 of the electrodes 22 are pulled out of the jack28. The removed assembly defines a cartridge C, which comprises thefilament 2l,'electrodes 22, insulating plate 23, doubling plate 25 andWehnelt electrode 24.

The cartridgeC is integrally and easily-detachable from the apparatusproper. In addition it is mechanically coupled to the apparatus by thefilament electrodes in contrast to conventional electron guns.

Before inserting cartridge C into jack 28, the filament tip 21a and thesmall hole 24a in the Wehnelt electrode can be preliminarily alignedwith each other by adjusting the position of the Wehnelt electrode 24with respect to the insulating plate 23, as described before. Inaddition, the cartridge is small, of simple construction, andmanufacturable'at low cost, which means that the whole cartridge C canbe easily changed for the purpose of a filament change.

To preventthe adhesion of metallic vapor from the filament 21 on theentire surface of the insulating plate 23 during use, thus causing shortcircuits between the filament electodes 22 or between the electrodes 22and the Wehnelt electrode 24, it is desirable to provide each electrode22 with a flange 22b, which is spaced from the insulating plate 23, orto provide an indented goove 24b along the internal base portion of theWehnelt electrode 24 which comes in contact with theinsulating plate 23.This increases the durability of the cartridge C by increasing thesurface distance between the electrodes 22 and the electrode 24.

The present inventionpermits a remarkable reducalignment of the filamentand the Wehnelt electrode even when the filament becomes heated.

As a result of said marked size reduction of the Wehnelt electrode, theWehnelt electrode, filament electrodes and supporting insulating platecan be manufactured at low cost in an integral cartridge which isreplacable as a whole when the filament must be replaced. Therefore, byaligning the Wehnelt electrode and the filament beforehand, when thecartridge is manufactured, the replacement of the filament iscomparitavely easy. 1

In addition, as a result of the use of a pair of electrodes with thespot-welded filament inserted in jacks on the electron gun insulator,the' whole electron gun has a more simplified construction and can bemade smaller in size than conventional electron guns. This, for example,permits the manufacture of bench scanning type electron microscopeswhichare easy to carry and install.

While preferred embodiments of the invention have been shown by way ofexample in the drawing, it will be understood that the invention is inno way limited to these embodiments.

What we claim is:

1. An electron gun for use in electron irradiation equipment, saidelectron gun comprising: a cartridge comprising a filament having twoplug terminals receptive of an electric potential applied thereto duringuse, a main electrode receptive of an electric potential applied theretoduring use for focusing electrons emitted by said filament, and mountingmeans having a major surface, said filament and said main electrodebeing disposed on said major surface and relatively positioned to effectfocusing by said main electrode of the electrons emitted by saidfilament; and means for removably mounting said cartridge includingsupply terminal means for supplying electric potential to said mainelectrode and said two plug terminals including jack means fordetachably coupling said two plug terminals both mechanically andelectrically to said supply terminal means and means separate from saidjack means for detachably, electrically coupling said main electrode tosaid supply terminal means whereby said cartridge may be detached fromsaid mounting means.

2. An electron gun according to claim 1, wherein said cartridge includesan electrically insulating plate member and means mounting said two plugterminals on said insulating plate member projecting therefrom on atleast one side thereof, said main electrode having a planar'baseportion, an electrically conductive plate member having means thereindefining two openings therethrough alignable with said two plugterminals and having a greater cross-sectional area than said two plugterminals to define a clearance thereabout, and mounting means mountingsaid insulating plate member between said base portion of said mainelectrode and said conductive plate member disposing said one side ofsaid insulating plate member facing said conductive plate member andaligning said two plug terminals with said two openings and forelectrically connecting said base portion to said conductive platemember.

3. An electron gun according to claim 2, wherein said mounting meanscomprises means defining a first pair of apertures in said base portionof said main electrode, means defining a second pair of apertures insaid insulating plate member aligned with said first pair of apertures,means defining a third pair of apertures in said conductive plate memberaligned with said second pair of apertures and having internal threads,and two threaded fasteners receivable in the three pairs of apertures tofasten said main electrode to said insulating and conductive platemembers.

4. An electron gun according to claim 3, wherein said means definingsaid second pair of apertures comprising means defining a clearanceabout each of said fasteners to permit adjustable movement of said mainelectrode with respect to said insulating plate member thereby providingfor the adjustable positioning of said main electrode with respect tosaid filament.

5. An electron gun according to claim 1, wherein said means forconnecting comprises means for adjustabily positioning said mainelectrode with respect to said filament.

6. An electron gun according to claim 1, wherein said main electrodecomprises a Wehnelt electrode.

7. An electron gun according to claim 2, wherein said base portion hasmeans therein defining a groove at the end portion thereof facing saidtwo plug electrodes and contacting said insulating plate member toincrease the surface distance between said two plug electrodes and saidbase portion.

8. An electron gun according to claim 1, wherein said means fordetachably coupling said main electrode comprises a resilient contactelectrically contacting said main electrode when said cartridge ismechanically coupled to said supply terminal means and means biasingsaid contact outwardly of said supply terminal means.

1. An electron gun for use in electron irradiation equipment, saidelectron gun comprising: a cartridge comprising a filament having twoplug terminals receptive of an electric potential applied thereto duringuse, a main electrode receptive of an electric potential applied theretoduring use for focusing electrons emitted by said filament, and mountingmeans having a major surface, said filament and said main electrodebeing disposed on said major surface and relatively positioned to effectfocusing by said main electrode of the electrons emitted by saidfilament; and means for removably mounting said cartridge includingsupply terminal means for supplying electric potential to said mainelectrode and said two plug terminals including jack means fordetachably coupling said two plug terminals both mechanically andelectrically to said supply terminal means and means separate from saidjack means for detachably, electrically coupLing said main electrode tosaid supply terminal means whereby said cartridge may be detached fromsaid mounting means.
 2. An electron gun according to claim 1, whereinsaid cartridge includes an electrically insulating plate member andmeans mounting said two plug terminals on said insulating plate memberprojecting therefrom on at least one side thereof, said main electrodehaving a planar base portion, an electrically conductive plate memberhaving means therein defining two openings therethrough alignable withsaid two plug terminals and having a greater cross-sectional area thansaid two plug terminals to define a clearance thereabout, and mountingmeans mounting said insulating plate member between said base portion ofsaid main electrode and said conductive plate member disposing said oneside of said insulating plate member facing said conductive plate memberand aligning said two plug terminals with said two openings and forelectrically connecting said base portion to said conductive platemember.
 3. An electron gun according to claim 2, wherein said mountingmeans comprises means defining a first pair of apertures in said baseportion of said main electrode, means defining a second pair ofapertures in said insulating plate member aligned with said first pairof apertures, means defining a third pair of apertures in saidconductive plate member aligned with said second pair of apertures andhaving internal threads, and two threaded fasteners receivable in thethree pairs of apertures to fasten said main electrode to saidinsulating and conductive plate members.
 4. An electron gun according toclaim 3, wherein said means defining said second pair of aperturescomprising means defining a clearance about each of said fasteners topermit adjustable movement of said main electrode with respect to saidinsulating plate member thereby providing for the adjustable positioningof said main electrode with respect to said filament.
 5. An electron gunaccording to claim 1, wherein said means for connecting comprises meansfor adjustabily positioning said main electrode with respect to saidfilament.
 6. An electron gun according to claim 1, wherein said mainelectrode comprises a Wehnelt electrode.
 7. An electron gun according toclaim 2, wherein said base portion has means therein defining a grooveat the end portion thereof facing said two plug electrodes andcontacting said insulating plate member to increase the surface distancebetween said two plug electrodes and said base portion.
 8. An electrongun according to claim 1, wherein said means for detachably couplingsaid main electrode comprises a resilient contact electricallycontacting said main electrode when said cartridge is mechanicallycoupled to said supply terminal means and means biasing said contactoutwardly of said supply terminal means.